This is the best lecture on the subject I've found! Can't wait for more MechE videos from you. Really grateful that you put the effort into doing this. Thanks a lot.
Your videos are so well put togehter that you can summarize à 45 minutes course in less than 10 minutes with all the informations needed. Very helpfull, thank you for this content
The most clear video about power screws on TH-cam. Bravo. If there is a backlash between the screw and the nut, so that there is an angle between the 2 axis (typical with a eccentric load), how would you quantify the additional resistive torque ?
A truly excellent presentation, resolving the virtual whole of one of the most common and often poorly attended issues of modern engineering. Having taken careful notes, explicitly because your presentation is so comprehensive, I did however notice a minor inconsistency, which I am sure, given your skills, is no more than an inadvertent editorial omission. The following is pasted directly from my notes; with the inconsistency relating to the radius r in your prescription for accounting for the frictional resistance of thrust bearings, beginning at 7:23: What is drawn as r is actually the outside diameter, odc, plus the inside diameter, idc, over 4. Thus for the nomenclature of the equation to stand, r must be re-defined as: r = (odc +idc) ÷ 4 [rather than dc ÷ 2] However, as this re-defined r is actually the mean radius of the "collar" (thrust bearing), it would probably be preferable to refer to the resultant r instead as the mean radius of the collar, mrc. Thus: mrc = (odc + idc) ÷ 4 FRICTION = fc × N = fc × F Tc = FRICTION × mrc or Tc = fc × F × ((odc + idc) ÷ 4) Where, if dimensions are expressed in meters and force is expressed in Newtons, the resultant torque, Tc, is expressed in Nm. [end of note] Again, many thanks for your excellent presentation. I wouldn't even go back and "fix" this, because anyone applying your excellent prescription will surely understand that you drew what you meant... and certainly meant for us to calculate what you meant. So, this would indeed be a very minor amendment. Keep up the great work.
There is very nice and short formula: Pr=F•tan(lamda+ phi), where phi is friction angle (tan(phi) = f). If phi > lamda, then the pitch is self-breaking.
The only difference between ACME and square thread profiles, in terms of the power screw torque equation, is that the secant of α is 1, as α = 0. The pitch and mean diameter are the same as in the 3 additional examples of this video. I will record one with square threads in about 2 weeks though. Links will be updated!
Can this be also applied for horizontal power screw? For example let’s assume we have a gripper that has to hold a weight and we need to know a minimum force required for the holding grip.
The maximum clamping force will depend on the maximum torque you're able to exert on the vise. That torque would be however much force you can push the handle with, times the length of the handle (the distance between where you're applying the force and the axis of rotation of the handle).
is the friction between the nut and screw used in the equation for torque raising the load or is it only collar friction or the friction of the bearing surfaces ?
Great video! But I didn't understand a thing: speaking about angled thread profiles, the force perpendicular to the thread flank shouldn't be F*cos(α) instead of F/cos(α)? F/cos(α) means that the perpendicular force is in modulus greater than the force you start with, am I missing something?
Yes, the force is larger: the force that you need to exert on the threads (through the torque) needs to be higher (F/cos(α)) so that the linear force, parallel to the screw and pushing it up or down is F. We want the relationship between the parallel force F, and the input torque T, not the normal [perpendicular] force to the surface of the threads. Also, input/output. Doesn't matter if torque or force is input/output.
@@LessBoringLecturesSo, what is FBD equation: F/cos(α) = F + what vector? What is the vector? What is the horizontal component? And why is it horizontal?
This is for lowering and lifting weights in vertical axis screw, is it same for horizontal alligned lead screw which is used in lathe machine ? Pls tell
The nut element is called that, because it's not necessarily an actual nut. It's just any element that is tapped/threaded. Therefore, the "nut element" won't rotate If it's a structure that is not allowed to rotate (physically).
No, pitch is just distance between two adjacent threads whereas lead is distance that a nut move wrt bolt per one revolution. However they are same for single thread screws and bolts but differ for multi thread screws and bolts.
α is the angle formed between the crests of two adjacent threads, as seen from a side view. λ is the lead angle, which refers to the angle of the slanted plane that threads follow, with respect to the plane that is perpendicular to the axis of the screw.
is dm the same as dp? i.e. (d+dr)/2 ??? It seems odd to me that frictional force is being calculated along the mean circumference (i.e. fn = f*Pi*dm) and not the mean thread area. The root diameter portion of the rod doesn't resist any friction. Only the threaded portion resists friction. So again, how come frictional force is being calculated along a linear path and not an aerial path?
The value for dm is only equal to dp for ACME or squared thread profiles. The friction does in fact affect the contact area at the threads, which for any location along the thread line, is a constant distributed load in the radial direction. This distributed load can in turn can be substituted by a point load for simplification purposes, without resulting in any difference in the final expression, whatsoever.
@@LessBoringLectures But what if your threads were extremely wide? Let's exaggerate so that I Illustrate my point. Let's assume the root diameter, dr, equals 1", but the main diameter, d, equals 10". That's an extremely wide thread that would amount to a much greater frictional force. Your calculation doesn't seem to take into account the thread width at all. Rather, your provided calculation considers the mean diameter, which, in my silly example would be 5.5" for an ACME thread. How come thread width isn't incorporated? What am I missing?
You got it right (you're not missing anything). The point load will in fact be found at 5.5 from the center. Friction is not dependent on surface area. This is a common physics misconception. More surface area does not mean more friction: as long as the normal force is the same, the friction force is the same. Pushing a box while on its smallest side is as hard as pushing it while on its largest side: pushing it requires the exact same force (as long as the surfaces are all made of the same material = meaning same friction coefficients).
@@LessBoringLectures wow. brilliantly explained. thank you! one final question. Is "F" the load on the entire bolt? Or is "F" the load on a single thread (or lead)?
@@markconverse927 No prob! F is the total load that affects all the "engaged threads". That's why we divide it into the number of engaged threads when calculating stresses at the threads: th-cam.com/video/46lcuQYQ14g/w-d-xo.html
This was beautiful. The sketches, the hand writing, the example, everything. This was absolutely beautiful.
This channel deserves more
This is the best lecture on the subject I've found!
Can't wait for more MechE videos from you.
Really grateful that you put the effort into doing this. Thanks a lot.
Glad it was helpful! Share with friends!
Your videos are so well put togehter that you can summarize à 45 minutes course in less than 10 minutes with all the informations needed. Very helpfull, thank you for this content
The most clear video about power screws on TH-cam. Bravo.
If there is a backlash between the screw and the nut, so that there is an angle between the 2 axis (typical with a eccentric load), how would you quantify the additional resistive torque ?
Man you described better than the textbook itself. Thank you so much.
A truly excellent presentation, resolving the virtual whole of one of the most common and often poorly attended issues of modern engineering.
Having taken careful notes, explicitly because your presentation is so comprehensive, I did however notice a minor inconsistency, which I am sure, given your skills, is no more than an inadvertent editorial omission. The following is pasted directly from my notes; with the inconsistency relating to the radius r in your prescription for accounting for the frictional resistance of thrust bearings, beginning at 7:23:
What is drawn as r is actually the outside diameter, odc, plus the inside diameter, idc, over 4. Thus for the nomenclature of the equation to stand, r must be re-defined as:
r = (odc +idc) ÷ 4 [rather than dc ÷ 2]
However, as this re-defined r is actually the mean radius of the "collar" (thrust bearing), it would probably be preferable to refer to the resultant r instead as the mean radius of the collar, mrc.
Thus:
mrc = (odc + idc) ÷ 4
FRICTION = fc × N = fc × F
Tc = FRICTION × mrc
or
Tc = fc × F × ((odc + idc) ÷ 4)
Where, if dimensions are expressed in meters and force is expressed in Newtons, the resultant torque, Tc, is expressed in Nm.
[end of note]
Again, many thanks for your excellent presentation. I wouldn't even go back and "fix" this, because anyone applying your excellent prescription will surely understand that you drew what you meant... and certainly meant for us to calculate what you meant. So, this would indeed be a very minor amendment.
Keep up the great work.
Thank for teaching, 10 min gives more than an hour of class lecture
Thanks a lot !!
Seriously you explained amazingly in 10 mins.
I can feel the hours of hardwork was dedicated to create such a wonderfull video lec.
This is exactly what I needed. Thank you!
Glad it was helpful!
There is very nice and short formula: Pr=F•tan(lamda+ phi), where phi is friction angle (tan(phi) = f). If phi > lamda, then the pitch is self-breaking.
Can't thank you enough for spreading such invaluable information. I am sure you would saving millions of grades!
More knowledge in less time👌
U deserve more support
Thank you! Share with your friends!
@@LessBoringLectures of course
perfect lecture🤟
can I access the file you wrote on it?
Good explanation
That saved me a lot of time, thanks.
Great video sir. Thank you!
You deserve way more subs and views
holy shit this is what i needed
Did you draw the friction in the right direction?
@LessBoringLectures Can you answer this please?
How are you writing so neatly digitally?
I'm using an apple Pencil on an iPad :)
Sir can i ask for simple square threaded problem for you to solve step by step? Hoping you could 🙏🙏
The only difference between ACME and square thread profiles, in terms of the power screw torque equation, is that the secant of α is 1, as α = 0. The pitch and mean diameter are the same as in the 3 additional examples of this video. I will record one with square threads in about 2 weeks though. Links will be updated!
Thank you!!
This is perfect, thanks!
Glad it helped!
Thanks very good
Great video.
Which software do you use for the animation?
For this video I was using WhiteBoard while recording the screen.
@@LessBoringLectures Thank you
Doesn’t it has to move clock wise to move the screw upward instead of anti clock wise
brother if we apply right hand rule ,then when we rotate it anti clock it should move up not downward🤔🤔
You're the best❤😍
Great job, thank you.
Nice video! What app are you using?
Thanks! I was using WhiteBoard back then
Can this be also applied for horizontal power screw? For example let’s assume we have a gripper that has to hold a weight and we need to know a minimum force required for the holding grip.
Good video until the end, you ruined it with the American units.
It's waooooo,,nice explanation
Hi sir. can u show sir for the double thread?
Sir can I ask how can you get the maximum clamping force, take for instance a bench vise , while you are neither given the torque nor force applied.
The maximum clamping force will depend on the maximum torque you're able to exert on the vise. That torque would be however much force you can push the handle with, times the length of the handle (the distance between where you're applying the force and the axis of rotation of the handle).
is the friction between the nut and screw used in the equation for torque raising the load or is it only collar friction or the friction of the bearing surfaces ?
Great video!
But I didn't understand a thing: speaking about angled thread profiles, the force perpendicular to the thread flank shouldn't be F*cos(α) instead of F/cos(α)?
F/cos(α) means that the perpendicular force is in modulus greater than the force you start with, am I missing something?
Yes, the force is larger: the force that you need to exert on the threads (through the torque) needs to be higher (F/cos(α)) so that the linear force, parallel to the screw and pushing it up or down is F. We want the relationship between the parallel force F, and the input torque T, not the normal [perpendicular] force to the surface of the threads.
Also, input/output. Doesn't matter if torque or force is input/output.
@@LessBoringLectures Thank you!
@@LessBoringLecturesSo, what is FBD equation: F/cos(α) = F + what vector? What is the vector? What is the horizontal component? And why is it horizontal?
Does this all apply to a horizontally driven lead screw?
This is for lowering and lifting weights in vertical axis screw, is it same for horizontal alligned lead screw which is used in lathe machine ? Pls tell
How does using multiple start threads affect load? For example a 1Nm torque on a 2 start 10mm thread gives a force of...?
This is great, can you recommend any papers or books on this subject ?
Shigley's Mechanical engineering design, perhaps the best book for this subject.
really usefull video
How the equation change with multiple starts?
Thanks
Which equation? Sorry for the late response.
4:04 what does guarantee that nut element won't rotate with the screw instead of translating?
The nut element is called that, because it's not necessarily an actual nut. It's just any element that is tapped/threaded. Therefore, the "nut element" won't rotate If it's a structure that is not allowed to rotate (physically).
@@LessBoringLectures thanks for your reply and for the high quality content.
Isn't the lead is the same as the Pitch?
No, pitch is just distance between two adjacent threads whereas lead is distance that a nut move wrt bolt per one revolution. However they are same for single thread screws and bolts but differ for multi thread screws and bolts.
I've watched some other vids on the topic and they used a reaction force, is the reaction force the normal and the friction added together?
Both the normal and friction forces can be considered reaction forces. But I wouldn't know exactly what they are referring to.
@@LessBoringLectures in their videos they only had 3 forces in the force diagram, but I think it was more elementary than what you are teaching.
is α equal to λ?
α is the angle formed between the crests of two adjacent threads, as seen from a side view. λ is the lead angle, which refers to the angle of the slanted plane that threads follow, with respect to the plane that is perpendicular to the axis of the screw.
is dm the same as dp? i.e. (d+dr)/2 ??? It seems odd to me that frictional force is being calculated along the mean circumference (i.e. fn = f*Pi*dm) and not the mean thread area. The root diameter portion of the rod doesn't resist any friction. Only the threaded portion resists friction. So again, how come frictional force is being calculated along a linear path and not an aerial path?
The value for dm is only equal to dp for ACME or squared thread profiles.
The friction does in fact affect the contact area at the threads, which for any location along the thread line, is a constant distributed load in the radial direction. This distributed load can in turn can be substituted by a point load for simplification purposes, without resulting in any difference in the final expression, whatsoever.
@@LessBoringLectures But what if your threads were extremely wide? Let's exaggerate so that I Illustrate my point. Let's assume the root diameter, dr, equals 1", but the main diameter, d, equals 10". That's an extremely wide thread that would amount to a much greater frictional force. Your calculation doesn't seem to take into account the thread width at all. Rather, your provided calculation considers the mean diameter, which, in my silly example would be 5.5" for an ACME thread. How come thread width isn't incorporated? What am I missing?
You got it right (you're not missing anything). The point load will in fact be found at 5.5 from the center. Friction is not dependent on surface area. This is a common physics misconception. More surface area does not mean more friction: as long as the normal force is the same, the friction force is the same. Pushing a box while on its smallest side is as hard as pushing it while on its largest side: pushing it requires the exact same force (as long as the surfaces are all made of the same material = meaning same friction coefficients).
@@LessBoringLectures wow. brilliantly explained. thank you! one final question. Is "F" the load on the entire bolt? Or is "F" the load on a single thread (or lead)?
@@markconverse927 No prob! F is the total load that affects all the "engaged threads". That's why we divide it into the number of engaged threads when calculating stresses at the threads: th-cam.com/video/46lcuQYQ14g/w-d-xo.html